Speed-limited ip fax method and a method for achieving gateway speed limitation in the ip fax

ABSTRACT

A method for limiting bit rate in IP facsimile, in this method the highest bit rate that the called gateway allows is determined, after the call connection is set up, the called electrograph transmits the digital identification containing the highest facsimile bit rate that the called electrograph provides, the called gateway compares the highest facsimile bit rate that the called electrograph provides with the determined highest bit rate that the called gateway allows, then selects the lower and inserts in the frame and transmits to the calling electrograph, the calling electrograph compares the bit rate with the highest bit rate that the calling electrograph itself provides, the lowest will be the highest bit rate at which message is transmitted, then the message is transmitted, confirmed, then the call connection is released. In this method, when the network becomes bad, the highest facsimile bit rate is limited through gateway to improve quality of pictures. A method for achieving limiting bit rate in IP facsimile by a gateway is also proposed in the present invention.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates to the field of IP facsimile, moreparticularly to an IP facsimile method for limiting bit rate in IPfacsimile. In addition, the present invention also relates to a methodfor limiting bit rate in IP facsimile by a gateway, which is the key ofthe technical effect of the method for limiting bit rate in IP facsimileaccording to the invention, and because it solves certain problems,having technical effect, it is proposed in the same applicant.

[0003] 2. Background of the Invention

[0004] Data is usually transmitted and switched through public switchedtelephone network (PSTN) in conventional facsimile technique. With thedevelopment of data communication and integrated service digitalnetwork, more and more facsimiles are transmitted by IP facsimile, i.e.,a message transmitter in the PSTN and a message receiver in the PSTN areconnected by Internet, and gateways are provided between thetransceivers in the PSTN and Internet to modulate and demodulate thedata of PSTN and IP data package.

[0005] IP facsimile can be classified to real-time IP facsimile andunreal-time one, i.e. IP storage transmission facsimile, IP real-timefacsimile. IP storage transmission facsimile means that when the gatewayreceives the time-division multiplexing data in the PSTN, it stores thedata in the transponder but not transmits the data instantly on theInternet after modulation, and when the callee needs receiving the data,such data is transmitted through the gateway. IP real-time facsimilemeans that when the gateway receives the time-division multiplexing datafrom PSTN, it transmits the data instantly on the Internet aftermodulation, it is real-time, which is conventionally used by us.

[0006] In the IP facsimile gateway, data are transmitted from PSTN toInternet or from Internet to PSTN, few control function is provided.

[0007] Conventional IP real-time facsimile comprises the followingsteps:

[0008] (1) A call connection is set up between the calling electrographand the called electrograph, the stage is as similar as the process ofthat of telephone call;

[0009] (2) The calling electrograph and the called electrographhandshake, the called electrograph sends a digital identification signalframe, and the highest facsimile bit rate provided by the calledelectrograph is in the information word of the digital identificationsignal frame;

[0010] (3) The calling electrograph takes out the bit rate from theinformation word after receiving the digital identification signalframe, then compares the bit rate with the highest bit rate provided bythe calling electrograph itself, then takes out the lower and inserts inthe digital command signal frame and sends it to the calledelectrograph, and this bit rate is as the highest bit rate at whichmessage is transmitted;

[0011] (4) Transmit the message;

[0012] (5) After the message is transmitted, process to the operation ofconfirmation, error-correction, continuous transmission for many pages;

[0013] (6) Release the facsimile call.

[0014] It is known from the implementing process of conventionaltechnique, the bit rate of conventional IP facsimile is controlledcompletely by the calling electrograph and the called electrographthemselves after handshaking, and it can not be controlled by outsideapparatus. Once jam happens on the Internet, the network performancewill become bad, therefore the higher facsimile bit rate the worsequality of pictures, which may cause unacceptable short line etc.Gateway users hope that when the network becomes bad, gateway can limitthe highest bit rate of the facsimile to improve the quality of thepictures and improve the reliability of IP facsimile. This is so-calledbit rate limit performance through gateway.

SUMMARY OF THE INVENTION

[0015] An object of the present invention is to provide a method forlimiting bit rate in IP facsimile and method for limiting bit rate by agateway, which ensures that when the network is not normal, the gatewaycan limit the highest bit rate of facsimile to improve the quality ofpictures, improve the reliability of IP facsimile.

[0016] To get above objects, the present invention provides a method forlimiting bit rate in IP facsimile, i.e. a message transmitter in a PSTNand a message receiver in other PSTN are connected by Internet, andgateways are provided between PSTNs of these transceivers and Internetto modulate and demodulate data between PSTN and IP data package,

[0017] a. Determine the highest bit rate that the called gateway allows;

[0018] b. The call connection between the calling electrograph and thecalled electrograph are set up through the PSTNs connected by Internet;

[0019] c. The calling electrograph and the called electrographhandshake, the called electrograph sends a digital identification signalframe to the called electrograph, and the highest facsimile bit rateprovided by the called electrograph is in the information word of thedigital identification signal frame, the called gateway takes out thebit rate from the information word after receiving the frame andcompares it with the determined highest bit rate that the called gatewayallows, if the bit rate is higher than the highest bit rate that thecalled gateway allows then the bit rate is amended to the highest bitrate that the called gateway allows, and if the bit rate is lower thanthe highest bit rate that the called gateway allows then the frame isnormally transmitted to the caller;

[0020] d. The calling electrograph takes out the bit rate from theinformation word of the frame after receiving the digital identificationsignal frame, then compares the bit rate with the highest bit rateprovided by the calling electrograph itself, then takes out the lowerand insert it in the digital command signal frame and sends it to thecalled electrograph, and this bit rate is as the highest bit rate atwhich message is transmitted;

[0021] e. The calling electrograph transmits message to the calledelectrograph;

[0022] f. After the message is transmitted, process to the operation ofconfirmation, error-correction, continuous transmission for many pages;

[0023] g. Release the call connection.

[0024] Preferably, in step a, the highest bit rate that the calledgateway allows is determined and the highest bit rate that the callinggateway allows is determined simultaneously; after step c, the callinggateway takes out the bit rate from the information word after receivingthe digital identification signal frame and compares the bit rate withthe determined highest bit rate that the calling gateway allows, if thebit rate is higher than the highest bit rate that the calling gatewayallows then the bit rate is amended to the highest bit rate that thecalling gateway allows, and if the bit rate is lower than the highestbit rate that the calling gateway allows then the frame is normallytransmitted to the calling electrograph.

[0025] Alternately, in step a, a man-machine interface is respectivelyprovided at the called gateway and the calling gateway, and the highestbit rate of the called gateway and the calling gateway can be input andstored in the storages of the called gateway and the calling gatewaythrough the man-machine interface; in step c, the called electrographtakes out the bit rate from the storages and compares it with the bitrate in the digital identification signal frame.

[0026] More preferably, in step a, a performance monitor is respectivelyprovided at the called gateway and the calling gateway to monitor thejam extent of the network in real time, and report the result to acontroller prestoring several determined threshold bit rate, eachthreshold bit rate corresponds to a type of data indicating jam extent,when the jam extent is monitored that it has reached the threshold levelthat another threshold bit rate corresponding to, the controllercontrols the new threshold bit rate to write into the storages of thecalled gateway and the calling gateway; in step 3, the bit rate is takenout from the storage to compare with the bit rate in the digitalidentification signal frame.

[0027] The present invention also discloses a method for achieving bitrate limit in IP facsimile by a gateway, gateways are provided betweenthe transceivers in the PSTN and Internet to modulate and demodulatedata between PSTN and IP data package,

[0028] a. Determine the highest bit rate that the called gateway allows;

[0029] b. The calling electrograph and the called electrographhandshake, the called electrograph sends a digital identification signalframe, and the highest facsimile bit rate provided by the calledelectrograph is in the information word of the digital identificationsignal frame, the called gateway takes out the bit rate from theinformation word after receiving the frame and compares it with thedetermined highest bit rate that the called gateway allows, if the bitrate is higher than the highest bit rate that the called gateway allowsthen the bit rate is amended to the highest bit rate that the calledgateway allows, and if the bit rate is lower than the highest bit ratethat the called gateway allows then the frame is normally transmitted tothe caller;

[0030] c. The calling electrograph takes out the bit rate from theinformation word of the frame after receiving the digital identificationsignal frame, then compares the bit rate with the highest bit rateprovided by the calling electrograph itself, then takes out the lowerand inserts it in the digital command signal frame and sends it to thecalled electrograph, and this bit rate is as the highest bit rate atwhich message is transmitted.

[0031] Preferably, in step a, the highest bit rate that the calledgateway allows is determined and the highest bit rate that the callinggateway allows is determined simultaneously; after step c, the callinggateway takes out the bit rate from the information word after receivingthe digital identification signal frame and compares the bit rate withthe determined highest bit rate that the calling gateway allows, if thebit rate is higher than the highest bit rate that the calling gatewayallows then the bit rate is amended to the highest bit rate that thecalling gateway allows, and if the bit rate is lower than the highestbit rate that the calling gateway allows then the frame is transmittednormally to the calling electrograph.

[0032] Because that a highest bit rate that the called gateway allows isdetermined according to the network state in the invention, the calledgateway compares the bit rate with the highest facsimile bit rate thatthe called electrograph allows in the digital identification signalframe, and the lower will be the highest bit rate that the callee andthe corresponding network can allow, then compares the bit rate with thehighest facsimile bit rate that the calling electrograph allows andselect the lower, therefore not only bit rate capacity of the callingand called electrograph but also the network performance and the bitrate it allows are in consideration, which ensures that when the networkbecomes bad, gateway can limit the highest-bit rate of facsimile toimprove the quality of pictures and improve the reliability of IPfacsimile.

[0033] More preferably, a highest bit rate that the calling gatewayallows is determined according to the network state, and the lower bitrate generated after the called gateway and the called electrographhandshake then handshake with the highest bit rate that the callinggateway allows, then select the lowest among the three, then compare thebit rate with the highest facsimile bit rate that the callingelectrograph allows at the calling electrograph side and select thelower, therefore not only the bit rate that the calling electrograph,called electrograph, the called network can allow but also that of thecalling network can allow are in consideration, therefore the highestbit rate of IP facsimile is further limited, the quality of pictures andreliability of IP facsimile are both improved.

[0034] In addition, a man-machine interface is respectively provided atthe called gateway and the calling gateway, and the highest bit rate ofthe called gateway and the calling gateway can be determinedartificially through the man-machine interface, therefore the highestbit rate that the network allows can be dynamically determined accordingto the concrete jam extent, in turn the quality of transmission can becontrolled flexibly.

[0035] Also, more preferably according to the invention, a performancemonitor is provided at the called gateway and the calling gateway tomonitor the jam extent in real time, and the highest bit rate that thecalled gateway and the calling gateway allow is dynamically adjusted inreal time according to the jam extent, therefore the highest bit ratethat the network allows can be dynamically adjusted in real timeaccording to the concrete jam extent of the network, in turn moreflexible control can be achieved.

BRIEF DESCRIPTION OF THE DRAWING

[0036]FIG. 1 is the flowchart of a method for limiting bit rate in IPfacsimile according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] The detailed description of the preferred embodiment of theinvention will be described in detail by referring to the drawing inFIG. 1, which is the flowchart of a method for limiting bit rate in IPfacsimile according to the invention, it is easy to be understood byreferring to the drawing in FIG. 1 and below description.

[0038] (1) Determining the highest bit rate that the called gatewaypermits, the bit rate must be one of six bit rates of 2400 bit/s, 4800bit/s, 7200 bit/s, 9600 bit/s, 12000 bit/s, 14400 bit/s, which areconventionally used in this field. In this step, the highest bit rate ofthe calling gateway can be initialized at the same time to one of sixbit rates, which bit rate is used usually depending upon below steps.

[0039] In the first mode, a man-machine interface is respectivelyprovided at the called gateway and the calling gateway, then the highestbit rate available for the called gateway and the calling gateway can beinput through the man-machine interface and stored in the storages ofthe called gateway and the calling gateway. Wherein, the networkperformance and jam extent are estimated by the network administrator,and which one of the six bit rates corresponding to the jam extent willbe estimated upon the jam extent and experience, then the bit rate willbe input to the man-machine interface and stored in the storages of thegateways to control. This method is realized artificially and thecontrol is not exact.

[0040] The second mode is based on statistics, the six bit rates and thecorresponding data range of jam extent of the network are both stored inthe controller, then a performance monitor is respectively provided atthe called gateway and the calling gateway to monitor the jam extent ofthe network in real time, which are reported to a controller, when thejam extent reaches to another threshold bit rate (one of the six), thecontroller writes the new threshold bit rate into the storages of thecalled gateway and the calling gateway. This method is realized uponstatistics and therefore more exact, which continuous monitoring andadjusting the net to enable flexible control according to the jam extentof the network.

[0041] (2) Setting up call connection between the calling electrographand the called electrograph through PSTN connected by Internet, i.e. thecalling electrograph initiates a call, then the calling gatewayidentifies destination address of this call, to set up a path to thecalled gateway for the called electrograph from the called gateway, whenthe called electrograph receives the call, a responding tone istransmitted back through the called and calling gateway, then a callconnection is set up. This process is much similar to that of telephonecall.

[0042] (3) The calling electrograph and the called electrographhandshake. Wherein the called electrograph sends a digitalidentification signal frame to the calling electrograph, and the highestfacsimile bit rate provided by the called electrograph is in theinformation word of the digital identification signal frame, the calledgateway takes out the bit rate from the information word after receivingthe frame, and compares it with the determined highest bit rate that thecalled gateway (said in step 1) allows, if the bit rate is higher thanthe highest bit rate that the called gateway allows then the bit rate isamended to the highest bit rate that the called gateway allows, and ifthe bit rate is lower than the highest bit rate that the called gatewayallows then the frame is normally transmitted to the caller;

[0043] If the highest bit rate that the calling gateway allows isdetermined in step 1, then in this step, the calling gateway takes outthe bit rate from the information word after receiving the digitalidentification signal frame and compares the bit rate with thedetermined highest bit rate (stored in the storage) that the callinggateway allows, which is said in step 1, if the bit rate is higher thanthe highest bit rate that the calling gateway allows then the bit rateis amended to the highest bit rate that the calling gateway allows, andif the bit rate is lower than the highest bit rate that the callinggateway allows then the frame is normally transmitted to the callingelectrograph.

[0044] For example, suppose that the highest facsimile bit rate that thecalled electrograph supports is 14400 bit/s, the called electrographtransmits the digital identification signal frame containing the bitrate information to the calling electrograph, the called gateway takesout the bit rate and compares it with the determined highest bit rate12000 bit/s that the called gateway allows, and finds that 12000 bit/sis lower than 14400 bit/s, then 14400 bit/s in the digitalidentification signal frame will be amended to 12000 bit/s, suppose thatthe highest bit rate that the calling gateway allows is not determinedin step 1, then the bit rate transmitted to the digital identificationsignal frame of the calling electrograph is 12000 bit/s.

[0045] Suppose that the highest facsimile bit rate that the callinggateway allows is 7200 bit/s, after receiving the digital identificationsignal frame containing 12000 bit/s, the calling gateway compares thebit rate 12000 bit/s with the determined highest bit rate 7200 bit/sthat the calling gateway allows, and finds that 7200 bit/s is lower than12000 bit/s, then 12000 bit/s in the digital identification signal framewill be amended to 7200 bit/s, therefore the bit rate transmitted to thedigital identification signal frame of the calling electrograph is 7200bit/s.

[0046] The called electrograph transmits the digital identificationsignal frame through the called gateway and the calling to the callingelectrograph and a sign bit and a called user's identification aretransmitted simultaneously, the called user's identification containsthe address of called electrograph, the typologic informationidentifying the state of called electrograph, after receiving theidentification, the calling electrograph transmits a delivering user'sidentification to the called electrograph through the calling gatewayand called gateway, the delivering user's identification contains theaddress of the calling electrograph, the typologic informationidentifying the state of calling electrograph.

[0047] After these steps, it is means that the calling electrograph andthe called electrograph have accomplished a handshake to determine thecapability on the called user's identification and the digitalidentification signal frame. Next, the calling electrograph transmits atraining signal to the called electrograph, and when receiving thebunch, the called electrograph compares the received bunch with theprestored training signal which is the same as the calling electrograph,then calculates the bit error rate (BER), and compares it with thepredetermined BER standard, if the BER is lower than the BER standard,then message can be transmitted, if the BER is higher than the BERstandard, then message can not be transmitted. The lasting time of thebunch is about 1.5±10% s, if the calling electrograph transmits a 0bunch containing 1000‘0’, the called electrograph receives 8 ‘1’ and 992‘0’, then BER is 0.8%, if the predetermined BER standard is 1%, 0.8%being smaller than 1%, then message can be transmitted.

[0048] (4) The calling electrograph takes out the bit rate from theinformation word of the frame after receiving the digital identificationsignal frame, then compares the bit rate with the highest bit rateprovided by the calling electrograph itself, then takes out the lowerand inserts it in the digital command signal frame and sends it to thecalled electrograph, and this bit rate is as the highest bit rate atwhich message is transmitted.

[0049] Suppose that the highest bit rate that the calling electrographprovides is 9600 bit/s, in the case that the highest bit rate that thecalling gateway allows is not determined in step 1, in the above casethe bit rate in the digital identification signal frame transmitted tothe calling electrograph is 12000 bit/s, 9600 bit/s being small than12000 bit/s, then the smaller 9600 bit/s is inserted in the digitalcommand signal frame and the frame is transmitted to the calledelectrograph, and this bit rate 7200 bit/s is as the highest bit rate atwhich message is transmitted.

[0050] (5) The calling electrograph transmits message to the calledelectrograph, and the process is known by the person of ordinary skillin the art, therefore it is not discussed here.

[0051] (6) After the message is transmitted, process to the operation ofconfirmation, error-correction, continuous transmission for many pages.During this process, when one or all pages of facsimile is finished, thecalling electrograph transmits the continuous transmission for manypages, finishing identifier to the called electrograph through thecalling, called gateway, after receiving the identifier the calledelectrograph transmits the continuous transmission for many pages,finishing confirmation identifier to the calling electrograph throughthe called, calling gateway.

[0052] (7) Release the call connection, this step corresponds to theprocess of setting up the call connection in step 2, and this part issimilar to the process of releasing the telephone call and is known bythe person of ordinary skill in the art, therefore it is not discussedhere.

[0053] Moreover, a method for limiting bit rate in IP facsimile by agateway is proposed in the present invention, this method corresponds tosaid steps 1, 3, 4, so it is not discussed here. The method is key torealize the technical effect of the method for limiting bit rate in IPfacsimile in the present invention, and because it has solved certaintechnical problems, having technical effect, they are proposed in thesame applicant.

What is claimed is:
 1. A method for limiting bit rate in IP facsimile,wherein a message transmitter in a PSTN and a message receiver in thePSTN are connected by Internet, and gateways being provided between thetransceivers in the PSTN and Internet to modulate and demodulate databetween PSTN and IP data package, a. determining the highest bit rateavailable for a called gateway; b. setting up call connection between acalling electrograph and the called electrograph via the PSTN connectedby the Internet; c. the calling electrograph and the called electrographhandshaking to determine the available highest bit rate, wherein thecalled electrograph sends a digital identification signal frame, inwhich an information word includes the highest facsimile bit rateprovided by the called electrograph, the called gateway taking out thebit rate from the information word after receiving the frame andcomparing the bit rate with the determined highest bit rate that thecalled gateway allows, if the bit rate being higher than the highest bitrate that the called gateway allows then the bit rate being amended tothe highest bit rate that the called gateway allows, and if the bit ratebeing lower than the highest bit rate that the called gateway allowsthen the frame being transmitted to the calling electrograph; d. thecalling electrograph taking out the bit rate from the information wordof the frame after receiving the digital identification signal frame,then comparing the bit rate with the highest bit rate provided by thecalling electrograph itself, then taking out the lower and inserting inthe digital command signal frame and sending to the called electrograph,and this bit rate being as the highest bit rate at which message istransmitted; e. the calling electrograph transmitting message to thecalled electrograph; f. after the message being transmitted, processingto the operation of confirmation, error-correction, continuoustransmission for many pages; g. releasing the call connection.
 2. Amethod for limiting bit rate in IP facsimile of claim 1, wherein in stepa, the highest bit rate that the called gateway allows and the highestbit rate that the calling gateway allows are determined simultaneously;after step c, the calling gateway taking out the bit rate from theinformation word after receiving the digital identification signal frameand comparing the bit rate with the determined highest bit rate that thecalling gateway allows, if the bit rate is higher than the highest bitrate that the calling gateway allows then the bit rate is being amendedto the highest bit rate that the calling gateway allows, and if the bitrate is lower than the highest bit rate that the calling gateway allowsthen the frame is normally transmitted to the calling electrograph.
 3. Amethod for limiting bit rate in IP facsimile of claim 1 or 2, wherein instep a, a man-machine interface is respectively provided at the calledgateway and the calling gateway, by which the highest bit rate of thecalled gateway and the calling gateway can be input and stored in thestorages of both the called gateway and the calling gateway; in step c,the called electrograph taking out the bit rate from the storage andcomparing with the bit rate in the digital identification signal frame.4. A method for limiting bit rate in IP facsimile of claim 1 or 2,wherein in step a, a performance monitor is provided respectively at thecalled gateway and the calling gateway to monitor the jam extent of thenetwork in real time, and the result being reported to a controllerprestoring with several predefined threshold bit rates, each of thethreshold bit rates corresponding to a jam extent, when the jam extentmonitored reaches another threshold bit rate, the controller writing thenew threshold bit rate into the storages of both the called gateway andthe calling gateway; in step c, the bit rate being taken out from thestorage to compare with the bit rate in the digital identificationsignal frame.
 5. A method for limiting bit rate in IP facsimile of claim1 or 2, wherein step b comprises: the calling electrograph initiating acall, then the calling gateway identifying destination address of thiscall, and setting up the path to the called gateway to the calledelectrograph from the called gateway, when the called electrographreceiving the call, a responding tone being transmitted back via thecalled and calling gateway to indicate a call connection having been setup.
 6. A method for limiting bit rate in IP facsimile of claim 1 or 2,wherein in step c, the called electrograph transmitting the digitalidentification signal frame via the called and the calling gateways tothe calling electrograph and transmitting a sign bit and a called user'sidentification, the called user's identification including an address ofcalled electrograph, a typologic information identifying the state ofcalled electrograph, after the identification being received, thecalling electrograph transmitting a delivering user's identification tothe called electrograph via the calling and called gateways, thedelivering user's identification including the address of the callingelectrograph, the typologic information identifying the state of callingelectrograph.
 7. A method for limiting bit rate in IP facsimile of claim6, wherein in step c, after the calling electrograph and the calledelectrograph handshaking upon the called user's identification and thedigital identification signal frame, the calling electrographtransmitting a training signal to the called electrograph, and when thebunch being received, the called electrograph comparing the receivedbunch with the prestored training signal which is the same as that inthe calling electrograph, and calculating the BER, comparing it with thepredetermined BER standard, if the BER being lower than the BERstandard, then message being transmitted, if the BER being higher thanthe BER standard, the message being not transmitted.
 8. A method forlimiting bit rate in IP facsimile of claim 1 or 2, wherein in the stepf, when one or all pages of the facsimile are transmitted, the callingelectrograph transmitting the continuous transmission for many pages,finishing identifier to the called electrograph through the calling,called gateway, after the identifier being received, the calledelectrograph transmitting the continuous transmission for many pages,finishing confirmation identifier to the calling electrograph via thecalled, calling gateway.
 9. A method for achieving bit rate limitthrough gateway, gateways are provided between transceivers in PSTN andInternet to modulate and demodulate data between PSTN and IP datapackage, a. determining the highest bit rate that the called gatewayallows; b. the calling electrograph and the called electrographhandshaking to determine the available highest bit rate, the calledelectrograph sending a digital identification signal frame, and thehighest facsimile bit rate provided by the called electrograph beingpackaged in the information word of the digital identification signalframe, the called gateway taking out the bit rate from the informationword after receiving the frame and comparing the bit rate with thedetermined highest bit rate that the called gateway allows, if the bitrate is higher than the highest bit rate that the called gateway allowsthen the bit rate being amended to the highest bit rate that the calledgateway allows, and if the bit rate is lower than the highest bit ratethat the called gateway allows then the frame being transmitted to thecaller; c. the calling electrograph taking out the bit rate from theinformation word of the frame after receiving the digital identificationsignal frame, then comparing the bit rate with the highest bit ratesupported by the calling electrograph itself, then taking out the lowerand adding to the digital command signal frame and sending to the calledelectrograph, and this bit rate being as the highest bit rate at whichmessage is transmitted.
 10. A method for achieving bit rate limitthrough gateway of claim 9, wherein in step a, the highest bit rate thatthe called gateway allows and the highest bit rate that the callinggateway allows are determined simultaneously; after step c, the callinggateway taking out the bit rate from the information word afterreceiving the digital identification signal frame and comparing the bitrate with the determined highest bit rate that the calling gatewayallows, if the bit rate is higher than the highest bit rate that thecalling gateway allows then the bit rate is amended to the highest bitrate that the calling gateway allows, and if the bit rate is lower thanthe highest bit rate that the calling gateway allows then the frame istransmitted normally to the calling electrograph.